Force Guest OS to Use 100Mbps/Full Duplex NIC

My service provider only provide 100Mbps/Full with no Auto-negotiate connection, therefore I have to make sure both host and guest are using 100Mbps/Full. While I know how to change it in the host, yet I am hitting some roadblock for CentOS, here is what I get.

# ethtool eth0

Settings for eth0:

        Supported ports:

        Supported link modes:   1000baseT/Full

        Supports auto-negotiation: No

        Advertised link modes:  Not reported

        Advertised auto-negotiation: No

        Speed: 1000Mb/s

        Duplex: Full

        Port: Twisted Pair

        PHYAD: 0

        Transceiver: internal

        Auto-negotiation: off

        Link detected: yes

# ethtool -s eth0 speed 100 duplex full

Cannot set new settings: Operation not supported

  not setting speed

  not setting duplex

Since  100 duplex full is not even in the support list, I can't change it. How can I force the gues OS to use 100Mbps/Full Duplex NIC?